(a) Field of the Invention
The present invention relates to an optical line terminal over a time division multiple access passive optical network and an optical signal processing method therefor.
(b) Description of the Related Art
Recently, a passive optical network (PON) technology has been deployed as an optical subscriber network technology for efficiently providing a variety of multimedia content.
A PON includes a subscriber side optical network unit (ONU) or optical network terminal (ONT), and an optical line terminal OLT for controlling the ONU or ONT. The PON has a Point-to-Multipoint (P2MP) communication structure in which an OLT splits an optical line into a plurality of optical lines by an optical splitter and a plurality of ONUs or ONTs are connected to the split optical lines.
The PON may be classified into a time division multiple access (TDMA)-PON and a wavelength division multiplexing (WDM)-PON according to a transmission scheme of downstream traffic from the OLT and upstream traffic from a subscriber side.
In the TDMA-PON, the OLT broadcasts all downstream traffic to be delivered to the subscriber, but the ONU or ONT transmits upstream traffic only in timeslots allocated to the ONU or ONT by TDMA. Such an upstream traffic transmission scheme is called a burst mode, and burst mode optical traffic transmitted from individual subscribers is different in amplitude and phase. Accordingly, the OLT requires a burst mode receiver capable of receiving burst mode optical traffic that is different in amplitude and phase from individual subscribers and processing it.
The burst mode receiver has a fast response to burst mode optical traffic from individual subscribers and a wide dynamic range, and requires high receiving sensitivity.
Traffic per optical line in the PON has been continuously increasing over the last 10 years. However, a transmission speed increase required for a traffic increase is physically accompanied by a decrease in the receiving sensitivity of the burst mode receiver and the ONU or ONT and an increase in optical line loss. Particularly, the use of a high-speed device at a subscriber's end is a major factor that increases overall network costs, and an increase in the speed of the burst mode receiver at the OLT leads to increased difficulty of technological development and decreased receiving sensitivity, resulting in system performance degradation.
Meanwhile, the PON may be advantageous in the miniaturization and simplification of a system because the number of parts used can be reduced by speeding up in terms of networks and systems. Accordingly, there is a need for a method that is suitable to optimize the economic efficiency and system performance throughout a network, which can minimize costs for a subscriber end, meet the requirements of system miniaturization and performance in the OLT, and minimize technical difficulty.